1. Field of the Invention
The present invention relates to an ink cartridge used in an ink jet printer, and an ink jet printer including an ink cartridge. Particularly, it relates to improvement of an ink cartridge and an ink jet printer that allows detection of the remaining amount of ink in the cartridge.
2. Description of the Background Art
An ink jet printer sprays out ink from a nozzle of a print head that moves parallel to an object to be printed to print out characters and images. A detachable ink cartridge as well as a nozzle are attached to the print head. The ink in the ink cartridge is sprayed out by pressurization means or electrostatic means.
When the amount of ink inside an ink cartridge is low, it is necessary to sense the low supply and identify the time to exchange the ink cartridge or to interrupt a printing process. A conventional ink jet printer and ink cartridge is provided with means to detect the amount of ink in the ink cartridge.
Means for detecting the remaining amount of ink includes a type that detects the amount of ink mechanically and electrically.
An ink jet printer will be described hereinafter including detecting means for mechanically detecting the remaining amount of ink. FIG. 36 is a perspective view of a structure of an ink cartridge of a first conventional ink jet printer. Ink is stored in an accommodating bag 101. Accommodating bag 101 is formed to contract in one direction according to decrease of the remaining amount of ink, and has a supply tube 102 for the outflow of ink. Accommodating bag 101 is placed in a box type cartridge case 103 with supply tube 102 projecting outwards. A plate 104 for detecting the remaining amount of ink is attached to the contraction region of accommodating bag 101 in cartridge case 103. A portion of plate 104 protrudes outward from a rectangular opening 105 formed in a longitudinal direction which is identical to the contraction direction of accommodating bag 101.
According to an ink cartridge of the above-described structure, plate 104 travels within rectangular opening 105 in response to the contraction of accommodating bag 101 as the remaining amount of ink becomes lower. A switch for detecting whether there is ink or not is provided in the main body of the ink jet printer to which this ink accommodating unit is loaded. When plate 104 travels a predetermined amount according to decrease of the remaining amount of ink, this switch is turned on to inform that the ink is exhausted.
A conventional ink jet printer having means for electrically detecting the remaining amount of ink will be described hereinafter. A conventional ink jet printer had electrodes provided in the proximity of an ink supply hole at the lower portion of an ink cartridge. A method is employed for detecting the remaining amount of ink by measuring the electrical resistance of the ink. According to this detection method, the electrical resistance between the electrodes increases when there is no ink around the electrodes. A low supply of ink can be identified according to the measured value of electrical resistance between the electrodes. Two types of ink jet printers detecting decrease in the amount of ink in an ink cartridge using such a detection method will be described hereinafter.
A second conventional ink jet printer including detection means for detecting electrically the remaining amount of ink will be described with reference to FIG. 37 showing a sectional view of an ink cartridge.
Referring to FIG. 37, an ink permeable sponge 4004 having a porous member impregnated with ink is installed in a container 4001. A pair of electrodes 4006 are provided at the lower portion of container 4001 as an out-of-ink sensor. An ink supply hole 4010 is provided at the lower portion of container 4001 communicating with a nozzle of a print head not shown. A pore is provided at the upper portion of container 4001. This pore 4011 supplies air into the ink cartridge to assist ink flow during the usage of the ink cartridge.
A third conventional ink jet printer having detection means for electrically detecting the remaining amount of ink is disclosed in Japanese Patent Laying-Open No. 3-277558. According to this ink jet printer, an ink accommodating unit includes an ink reservoir having a porous material for impregnating ink and an ink fountain communicating with the ink reservoir. Ink is supplied to a print head from the ink fountain.
Electrodes are provided in a portion of the porous material in the ink reservoir and in a portion of the ink fountain. A remaining amount detection unit is provided for detecting the remaining amount of ink according to the change in resistance between the electrodes.
When ink in the ink accommodating unit becomes nearly exhausted in the ink jet printer of the above-described structure, air will be introduced into the joint portion between the ink reservoir and the ink fountain to reduce the area of the joining portion, whereby resistance between the electrodes suddenly increases.
In this ink jet printer, the characteristics of the relationship between the remaining amount of ink and the resistance between the electrodes is obtained previously, and the value of the change in resistance when the ink is near exhaustion is previously set in the remaining amount detection unit. In the remaining amount detection unit, the change in the resistance between the electrodes is detected, whereby that change and a preset value of change are compared. Determination is made that the ink is near exhaustion when the values match.
The above-described conventional ink jet printers have problems as set forth in the following regarding detection of the remaining amount of ink. The above-described first conventional ink jet printer detecting mechanically the remaining amount of ink had a problem that the detection precision is low since the deformation characteristics of accommodating bag 101 differs from bag to bag.
In the ink cartridge of the above-described second conventional ink jet printer, sufficient spacing between electrodes 4006 is necessary in order to detect reduction of the amount of ink on the basis of increase in electrical resistance between electrodes 4006. If the spacing between electrodes 4006 is not sufficient, ink will remain between the electrodes, leading to a problem that decrease in ink could not be detected. Also, there is a problem that the size of the ink cartridge could not be reduced. Furthermore, when ink is permeated into a sponge or the like, there was a possibility of decrease in the amount of ink not being able to be detected due to residue ink in the sponge.
In the third conventional ink jet printer detecting electrically the remaining amount of ink, the characteristics of the relationship between the remaining amount of ink and the resistance is non-linear. Detection of the remaining amount of ink on the basis of comparison between a measured value and a set value of the change in resistance obtained by such characteristics was not reliable, leading to a problem of low detection accuracy. There was also a problem that the structure of the ink remaining amount detection system is complicated since the measured value and the set value regarding the change of resistance have to be continuously compared.